The present invention relates generally to a method of operating an engine, and more particularly to a method of reducing nitrogen oxide emission during operation of an engine by using a fuel mixture therein which includes a gaseous fuel and an emulsified pilot fuel.
Engines capable of operating on two different types of fuels are referred to as dual fuel engines. One type of dual fuel engine is a diesel engine designed to have two operating modes. Specifically, in the first mode of operation the diesel engine is run on diesel fuel alone. In the second mode of operation the diesel engine utilizes natural gas as the primary fuel and the natural gas is ignited by a diesel pilot fuel within the combustion chamber of the engine.
Operating the engine with a mixture of natural gas and diesel pilot fuel provides a number of advantages as compared to operating the engine with diesel fuel alone. For example, a mixture of natural gas and diesel pilot fuel is less expensive than a comparable amount of diesel fuel alone. Therefore, operating the engine with a natural gas/diesel pilot fuel mixture is less expensive as compared to operating the engine with diesel fuel alone.
Another advantage of operating the engine with a mixture of natural gas and diesel pilot fuel is that combustion of a natural gas/diesel pilot fuel mixture results in a smaller amount of nitrogen oxides (NOx) being produced as compared to combustion of a comparable amount of diesel fuel alone. Thus, operating the engine with a natural gas/diesel pilot fuel mixture results in less NOx being produced as compared to operating the engine with diesel fuel alone.
While the use of a natural gas/diesel pilot fuel mixture in the operation of an engine provides the significant advantages mentioned above, such use still results in the production of NOx, albeit a substantially reduced amount. It is a known goal to reduce the production of NOx as much as possible. Thus, it would be desirable to even further reduce the production of NOx which results from the operation of an engine.
In accordance with a first embodiment of the present invention, there is provided a method of reducing production of nitrogen oxides during operation of an engine, with the engine having a combustion chamber. The method includes the steps of (i) advancing air into the combustion chamber, (ii) advancing a gaseous fuel into the combustion chamber, (iii) injecting an emulsified pilot fuel into the combustion chamber, wherein the emulsified pilot fuel includes water and liquid fuel, and (iv) compressing a mixture which includes (A) the air, (B) the gaseous fuel, and (C) the emulsified pilot fuel within the combustion chamber during a compression stroke of the engine, whereby heat generated by compression of the mixture causes the emulsified pilot fuel to combust so as to ignite the gaseous fuel.
In accordance with a second embodiment of the present invention, there is provided a method of reducing production of nitrogen oxides during operation of an engine, with the engine having a combustion chamber. The method includes the steps of (i) advancing air and a gaseous fuel into the combustion chamber during an air intake stroke of the engine, (ii) injecting an emulsified pilot fuel into the combustion chamber during a compression stroke of the engine, wherein the emulsified pilot fuel includes water and diesel fuel, and (iii) compressing a mixture which includes (A) the air, (B) the gaseous fuel, and (C) the emulsified pilot fuel within the combustion chamber during the compression stroke of the engine, whereby heat generated by compression of the mixture causes the emulsified pilot fuel to combust so as to ignite the gaseous fuel.